Typically, magneto-resistive (XMR) sensors include one or more XMR sensing or sensor elements for measuring a magnetic field. XMR sensor elements include anisotropic magneto-resistance (AMR) sensor elements, giant magneto-resistance (GMR) sensor elements, tunneling magneto-resistance (TMR) sensor elements, and colossal magneto-resistance (CMR) sensor elements.
Sometimes, in speed sensors, a permanent magnet is attached to a magnetic field sensor that includes multiple XMR sensor elements. The permanent magnet provides a back bias magnetic field for the multiple XMR sensor elements. The magnetic field sensor is placed in front of a toothed magnetically permeable wheel or disk. As the disk rotates, the teeth pass in front of the magnetic field sensor and generate small field variations in the magnetic field. These small field variations are detected by the XMR sensor elements and include information about rotational speed and angular position of the rotating disk.
However, a small misplacement of the back bias magnet or diverging magnetic field lines of the back bias magnetic field may result in magnetic field components that adversely affect the XMR sensor elements. These magnetic field lines may drive the XMR sensor elements into saturation and render the XMR sensor elements useless for detecting variations in the magnetic field.
For these and other reasons there is a need for the present invention.